Incorrect addons project after upgrade from Gramps 5.2

[prculley]

Upgrades from older Gramps (Gramps v5.2.x) copy the gramps.ini from the older version, including the "behaviour.addons-projects" values, which then point to the older github addons. This fixes that.

Fixes #13789.

[emyoulation]

Addresses https://gramps-project.org/bugs/view.php?id=13789

[emyoulation]

Instead of resetting to defaults, could this just deselect all but the 1st (default) "Project" rather than flushing the row? (Upgrade warning dialogs are generally undesirable since they disrupt the workflow but... perhaps pop a Warning on gramps.ini import that Addon "Projects" need to be updated?)

This would allow users to Edit the URL to a current version path without having to find the URL or remember which Projects that they had added.

Also, if the Addon Manager becomes smarter about not trying to install gramps_target_version addons that are mismatches, then the JSON might have mixed sets of gramps_target_version rows. ( I do not know how the "major_version" hack in Isotammi .gpr.py will work/fail with smarter gramps_target_version attribute handling.)

Also, if a URL Validator enhancement (as suggested in 13069) is added, then this routine could 'invalidate' as well as deselect project rows.

There are a series of Addon Manager feature requests and bugs (with some duplication) linked to:
https://gramps-project.org/bugs/view.php?id=13069